Transducers, such as for hearing aids, typically include a motor to drive a diaphragm, all disposed within a housing. The motor typically includes a coil, a yoke, such as a stack and an armature, which together form a magnetic circuit. It is often desired to contain electromagnetic flux generated by the magnetic circuit within the transducer. This is especially important when the transducer is used in conjunction with a hearing aid having a telecoil, as the flux can adversely affect the performance of the telecoil. In such circumstances, the transducer housing typically is made of magnetically shielded material and completely encases the motor. Because the housing completely encases the motor components, however, size reduction of the transducer has been hampered.
In certain applications where flux leakage is not a significant concern, the stack is exposed and positioned between two end caps, which contain the remaining components of the transducer. Such a transducer is disclosed in Knowles Electronics Inc.'s published PCT application WO 95/07014. However, this transducer can exhibit reduced mechanical strength because of the joints forming the exterior shell, i.e., the stack joined to the end caps.
The present invention is provided for these and other problems.